The invention relates to an apparatus for applying a thin layer of a coating material to a web of material passing over a counter-pressure roller, with a slot nozzle device, which comprises a vertical nozzle box with a wide upper nozzle slot between inlet and outlet nozzle lips and a storage tank for coating material mounted laterally on the nozzle box. In a coating apparatus of this kind, the thickness of the layer applied is essentially determined by the distance between the outlet nozzle lip and the web of material or counter-pressure roller.